The present invention relates to a scroll type compressor for compressing refrigerant, which is a part of a refrigerant circuit of an air conditioner.
In such a scroll type compressor, the housing includes a fixed scroll member, which has a fixed base plate and a fixed scroll wall that extends from the fixed base plate, and a movable scroll member, which has a movable base plate and a movable scroll wall that extends from the movable base plate and engages with the fixed scroll wall. By the orbital motion of the movable scroll member with the self-rotation thereof being blocked, compression chambers defined between the fixed scroll wall and the movable scroll wall move radially and inwardly to progressively reduce their volumes, thus compressing refrigerant gas.
Recently, carbon dioxide has generally been employed as refrigerant for the refrigerant circuit. Pressure in the refrigerant circuit when employing carbon dioxide as refrigerant is higher than that when employing fluorocarbon as refrigerant. Accordingly, in a scroll type compressor, unusually large thrust force is applied to the movable scroll member based upon the high pressure in the compression chamber. Then, the movable scroll member slides under the hard condition, and durability of the scroll type compressor is deteriorated.
In order to solve such problems, according to pages 4 and 5, and FIG. 1 of Unexamined Japanese Patent Publication No. 2000-249086, the movable scroll member forms a recess on its back surface of the movable base plate, and the recess is closed by a fixed wall on the back surface side provided in the housing, thus defining a back pressure chamber. The compression chamber during volume-reducing process is in communication with the back pressure chamber through a supply passage. High-pressure refrigerant gas is introduced from the compression chamber into the back pressure chamber through the supply passage. In the movable scroll member, a check valve is arranged in the supply passage for blocking the refrigerant gas from back-flowing from the back pressure chamber to the compression chamber.
Accordingly, the pressure in the back pressure chamber applies back pressure force, which opposes thrust force based upon the pressure in the compression chamber, to the movable scroll member. Thus, sliding resistance is reduced between the movable base plate of the movable scroll member and the fixed wall on the back surface side, on which the back surface of the movable base plate slides.
The pressure in the back pressure chamber, that is, the back pressure force applied to the movable scroll member, is appropriately adjusted so that the clearance (passing cross-sectional area of the refrigerant gas) between the movable base plate of the movable scroll member and the fixed wall on the back surface side varies. In other words, for example, as the pressure in the compression chamber rises, the thrust force applied to the movable scroll member increases, with the result of the minimum (zero) clearance between the movable base plate and the fixed wall on the back surface side. Accordingly, the refrigerant gas is blocked from being bled from the back pressure chamber to the suction pressure region through the clearance, and the pressure in the back pressure chamber, that is, the back pressure force applied to the movable scroll member tends to increase.
On the contrary, as the pressure in the compression chamber falls, the thrust force applied to the movable scroll member decreases, with the result of the increased clearance between the movable base plate and the fixed wall on the back surface side. Accordingly, the amount of refrigerant gas bled from the back pressure chamber to the suction pressure region through the clearance increases, and the pressure in the back pressure chamber, that is, the back pressure force applied to the movable scroll member tends to decrease.
Then, the valve-opening operation of the check valve bleeds the refrigerant gas in the back pressure chamber to the suction pressure region before the high-pressure refrigerant gas in the compression chamber is bled to the back pressure chamber. Accordingly, the movable scroll member instantaneously contacts the fixed wall on the back surface side with its movable base plate by the thrust force, so that the high-pressure refrigerant gas in the compression chamber, that is, the refrigerant gas that has finished its compression work is prevented from uselessly flowing out to the suction pressure region through the supply passage and the back pressure chamber. This leads to improved efficiency of the scroll type compressor.
In the Unexamined Japanese Patent Publication No. 2000-249086, in addition to the clearance (a portion that functions as a valve) between the movable base plate and the fixed wall on the back surface side, the check valve needs to be arranged in the supply passage in the movable scroll member, therefore, there has particularly been a problem that it needs much effort to assemble the check valve to the movable scroll member. That is, in the Unexamined Japanese Patent Publication No. 2000-249086 with the complicated valve structure for adjusting the back pressure, there has been a problem that it needs much cost and work for manufacturing a scroll type compressor. Therefore, there is a need for providing a scroll type compressor that has a simple valve structure for adjusting back pressure force.